1. Field of the Invention
The present invention relates to a light emitting diode used for illuminating a variety of electronic devices and also in recent years for illuminating panel meters of automobiles, and in particular, relates to a light emitting diode provided with a reflection cup to give an illuminating light a desired directivity.
2. Description of Related Art
An example of light emitting diode of this kind is disclosed in Japanese Patent Disclosure No. 2002-324917. This light emitting diode, as shown in FIG. 1, comprises a base substrate 2 surface-mounted on a mother board 1, a light emitting element 3 put on an upper surface of the base substrate 2, a reflection cup 4 arranged to surround the light emitting element 3, a resin sealant 5 sealing the light emitting element 3 and the reflection cup 4, and a dome-shaped light collecting member 6 placed on the resin sealant 5.
In such a light emitting diode, light emitted from the light emitting element 3 is reflected by an inner circumferential surface of the reflection cup 4 to be given an upward directivity and then passes through a lens portion 6a of the light collecting member 6 to have a stronger directivity.
In recent years, there is a growing demand for a light emitting diode with a so-called narrow directivity, which focuses light emitted from a light emitting element and illuminates the focused light on a point. To realize such a narrow directivity, it is desired, as shown in FIG. 2, that an inner circumferential surface 7 of the reflection cup 4a be formed in a paraboloidal shape, with the light emitting element 3a disposed at a focus of the paraboloid. With this arrangement the light emitted from the light emitting element 3a can be collimated into upward parallel rays when reflected by the inner circumferential surface 7 of the reflection cup 4a. Thus, an inner circumferential edge 9 at the lower end of the reflection cup 4a near the light emitting element 3a is preferably formed into a sharp inclined shape 10 that smoothly merges with the paraboloidal surface of the inner circumferential surface 7.
However, when the reflection cup 4a is formed by a plastic material, the sharp inclined shape 10 is difficult to form along the inner circumferential edge 9 of the cup and in practice the end of the inner circumferential edge 9 is deformed or rounded. Especially when the light emitting element 3a is flip-chip mounted, since a lower end 12 of a light emitting face 11 of the light emitting element 3a is very close to an upper surface of the base substrate 2, only about a few tens of μm apart, the shape of the inner circumferential edge 9 has a significant effect on the reflection of light. When the light emitted from the light emitting face 11 of the light emitting element 3a strikes the inner circumferential edge 9 at the lower end of the reflection cup 4a, the light is scattered, rendering the control of narrow light directivity difficult. The above problem is also experienced when the reflection cup 4a is formed by press-forming a metal material.